Do you actually have a 600 bp band, or you have a problem telling you that a 600 bp band is generated by PCR?
I Googled the vector, and it's 3kb w/o insert.
I'm don't know if the primer positions you give are with or w/o insert. OK, I looked that up too in a manual, and you gave the positions without any insert. Judging by the other primers I saw on a map, the positions they give are regardless of the fact that the second primer is actually a reverse primer, they didn't reverse the positions of start and stop to show this.
So, find the size of the PCR product with vector only, and subtract this from the PCR product size to find the insert size. To find the vector only size, since you are going around the corner of the 3000 / 1 numbering origin, you can add up the size of M13rev - 3000bp positions, (3000-2940), + the 177bp furthest position on the other side of the zero position. Understand?
I think your nightmare revolved around the fact that by the positions they give for both primers, it looks like they are both oriented forwards, and could not make a PCR product. However, on the diagram of the thing, the SP6 and T7 primers are shown facing toward each other, while in the text they are also indicated the same as the M13 primers, as if they are both forward primers. So, the text shows the position of the primer, but this does not indicate the orientation. Just assume that if they are facing each other to function in PCR, that you calculate that the PCR product extends from the lowest number (well, it's highest since the cloning site crosses the zero position. Maybe that was the other source of confusion) to the highest number.